The subject matter of the present invention pertains to a logic analyzer having search and comparison capabilities.
In various kinds of electronic apparatus, logic techniques are increasingly popular as a result of developments of microprocessors and computers. Oscilloscopes, logic probes and logic analyzers are utilized for developing, calibrating and trouble-shooting an electronic apparatus using these logic techniques. A logic analyzer is especially ideal for use as a measurement instrument of such electronic apparatus, because it can store multi-channel input logic signals (data) in a memory, such as a random access memory (RAM) and display the data stored in the memory on a display means, such as a cathode ray tube (CRT), so that the displayed data (before a trigger signal occurence) may be measured. There are two display modes used by a logic analyzer; one is a timing display mode for displaying the logic signals as signal waveforms; the other is a state display mode for displaying the stored data as characters (alphanumerics) of words, such as binary, octal and hexadecimal. In the state display mode, data stored in only selected addresses of the memory are displayed. All of the data stored in the memory cannot be displayed simultaneously because of the relationship between a display area and the sizes of the characters to be displayed.
Conventional logic analyzers have many functions, and one of them is a search function (or search mode). This mode is frequently selected especially in the state display mode, wherein a search word set by an operator is detected from the data stored in the memory. The searched word and the memory address thereof are displayed on a first line, and a predetermined number of words followed by this address are displayed on the following lines thereby constituting a state table. However, since all the data stored in the memory cannot be displayed in the state display mode as described hereinbefore, it is difficult to know a total number of the search words included in all the data and a relation between the total number and the search words displayed on the display means. As a result, measurement is troublesome. On the other hand, the search mode is not available in the timing display mode, so that it is troublesome to measure a timing relation among a plurality of logic signals with respect to a desired word.
Another function of a conventional logic analyzer is the detection of a glitch (a narrow width pulse signal which affects the operation of logic circuits). The glitch can be detected if a clock frequency is increased when storing the input logic signal in the memory. However, the glitch is detected commonly by a glitch detector consisting of logic circuits, such as latch circuits or the like, since the maximum clock frequency is limited by the characteristics of the memory. The detected glitch is displayed as a pulse of one bit width in the timing display mode (the glitch intensity is sometimes modulated). It is difficult to know a total number of the glitches in all the data stored in the memory and a relationship between the total number and a glitch displayed on the display means. As a result, measurement is inconvenient. Moreover, conventional logic analyzers cannot display the glitch in the state display mode. Therefore, it cannot be determined whether or not the displayed data includes the glitch.
The conventional logic analyzers have a further function, a comparison function (or comparison mode). This function is especially used in the state display mode, wherein the input logic signals stored in a first memory are compared with reference logic signals stored in a second memory and one or both of the input and reference logic signals are displayed on the display means. Conventional logic analyzers modulate the intensity of different parts of the input and reference logic signals, invert the different parts (inversion between white and black) or add markers to the different parts for distinguishing between the different parts of the input and reference logic signal from other parts thereof (easy measurement). Since all the data stored in the memory cannot be displayed simultaneously in the state display mode as described hereinbefore, it is difficult to know a total number of the different (or other) parts of the input and reference logic signal included on the display means, namely, a relationship between all the data and the displayed parts. Thus, measurement is troublesome.